Retroreflective sheet material is widely employed for a variety of safety and decorative purposes, and is particularly useful when the need for night time visibility is significant under conditions of low ambient light. In retroreflective materials, the light rays impinging upon the front surface are reflected back towards the source of the illumination in a substantially parallel path. In situations where headlights or search lights on boats and aircraft are the only source of illumination, this ability to retroreflect the bulk of the rays falling thereon is especially significant for warning signs.
Among the applications for such retroreflective materials are reflective tapes and patches for clothing of firemen, reflective vests and belts, bands for posts and barrels, traffic cone collars, highway signs, warning reflectors, and the like.
In U.S. Pat. No. 4,801,193 granted Jan. 31, 1989 (incorporated herein in its entirety by reference), there is described in detail a partially retroreflective sheet producing process in which grid patterns of metallized and unmetallized prisms are formed, and the use of adhesive spacing to provide an air backing for unmetallized prisms.
U.S. Pat. No. 5,229,882 granted Jul. 20, 1993 (incorporated herein in its entirety by reference) describes in detail a process for producing retroreflective microprism material providing a visual coloration, wherein some of the microprisms have a retroreflective interface and the remainder have a colored non-reflective coating thereon.
As a result, light rays entering the front or base face which impinge upon the prism side facets having retroreflective interfaces are redirected so that they exit the material in a parallel path i.e. retroreflect. Light rays which travel to the facets of color coated prisms are refracted from those prisms and impart a visual coloration to the material in daylight and ambient light.